How to set up Time Machine backups to an external USB drive

October 21, 2011 in Mac OS X

There are two types of people in the world: Those who have forever lost important computer files, and those who haven’t…YET! Most people in the first group have learned their lesson (the hard way) and are now backing up their computer on a regular basis. If you are in the second group you have two options:

  1. Experience a painful loss of important photos, videos, music, emails and documents, and THEN start backing up, or
  2. Learn from the first group and start backing up your computer NOW!

It’s your choice, but don’t say you haven’t been warned. All hard drives will fail, it’s just a question of when. Even computer geeks accidentally delete a folder of important files when they meant to delete something else. If you back up your computer regularly and correctly, these otherwise devastating catastrophes become a minor hurdle that you can overcome quickly. And you’ll pat yourself on the back for being so intelligent for having a good computer backup.

External hard drives are a great way to back up your computer and they are now amazingly cheap. In this video I show you how easy it is to plug one into your computer and quickly set up the Time Machine application that comes with your Mac. You’ll be breathing easier in no time at all.

Video too small? Watch full screen by clicking the YouTube Full Screen button button here

What Time Machine does

There are many backup applications out there and many perform most of the functions of Apple’s Time Machine. Your external drive may have even come with backup software. I wouldn’t bother with it. What Time Machine has going for it is it:

  • Keeps previous versions of files that have changed;
  • Lets you browse and recover old files from the Finder and also directly from other Apple applications like iPhoto, Address Book, Mail;
  • Is FREE!

Time Machine doesn’t make a full backup of your computer every time it runs. It only does a full backup the first time. After that, it’s intelligent and only copies the files that have changed (this is called an “incremental backup”). As you’ll see in its preferences window, Time Machine keeps:

  • Hourly backups for the past 24 hours
  • Daily backups for the past month
  • Weekly backups for all previous months

The only constraints on how far back these backups go are the capacity of your backup drive and how big each incremental backup is. If you mainly use your computer for surfing the web, each hourly backup will likely be small (and quick) and your Time Machine backups will ultimately go far back in time. But if you download, create, or edit lots of big video files and your backup drive isn’t a lot bigger than your internal drive, your Time Machine backups won’t go back as far. In that case, you’ll still have a backup copy of every file, you just won’t have as many historical versions of them.

Setting up Time Machine

Before setting up Time Machine, you first need to plug your external drive into your computer. It’s perfectly fine to plug in an external drive while your computer is on. (But do NOT unplug it without reading the important instructions later in this article.)

New external drives often show up on your Desktop with the brand name and model (for instance, in the above video, mine is “WD Passport”). The first thing I like to do is change that name to something that describes what I’m using the drive for. This is especially useful if you ever have more than one of these drives. It will make it immediately obvious which is your Time Machine Backup and which is your iTunes Music Library. You can change the drive’s name by clicking on the name under the drive’s icon and holding for two seconds. When you let go of your click, the drive’s name should be highlighted and editable. Just type the new name and hit Enter.

You can start configuring Time Machine by clicking on its icon if it’s on your Dock, or launching System Preferences and clicking on the Time Machine icon there. You tell Time Machine which drive to use for backups by clicking the “Select Backup Disk…” button, selecting your newly plugged in drive, then clicking the “Use for Backup” button. Time Machine will schedule your first backup to start in just two minutes. If you want Time Machine to back up your whole internal drive (and in almost all cases this is what you should want), then you can just sit back and wait for Time Machine to do its thing.

If you need to exclude some items from your Time Machine backup, you can do that by first clicking on the “Options…” button, then clicking the “+” button, and choosing which folders or files you want to exclude. Normally you’d want to backup everything just in case. Some reasons to exclude items from your backup are:

  • Your external backup drive is not big enough to back up your whole internal drive;
  • You have folder(s) of temporary files you know you will never need and that change frequently (meaning they’ll slow down each backup process with updated files you’re never going to want)
  • You already have backups for a specific folder and want to leave more space in Time Machine for more historical copies of your other stuff.

Time Machine on the menu bar

Before closing the Time Machine preferences window, I like to check the “Show Time Machine status in the menu bar” box. That will put a little Time Machine icon Time Machine menu bar icon on the right side of your menu bar. This is a handy place to:

  • Check Time Machine’s status (either the time of its last backup, or its progress on a currently running backup);
  • Manually start a backup before the next scheduled time using the “Back Up Now” option;
  • Stop a backup in progress using the “Stop Backing Up” option (not recommended, but sometimes you just have to eject your drive and pick up your laptop);
  • Access to the Time Machine Preferences window;
  • “Enter Time Machine” to actually see what files were on your computer in the past and recover them if necessary.

Even though Time Machine will perform a backup every hour, I still sometimes use the “Back Up Now” option. It’s really handy if I’ve just completed some brilliant work and need to grab my laptop and go somewhere. It gives me peace of mind knowing that I’m not carrying the only copy of my work in my MacBook Pro that can be stolen, dropped, or have coffee spilled on it.

Time Machine problems

Time Machine usually runs nearly silently and invisibly with no problems. Just make sure you don’t unplug your external drive without ejecting it, and try to not shut down or put your computer to sleep during a backup process (although it will usually recover even from that). The most likely problem you may see is the “Time Machine could not complete the backup” popup window with the dreaded message that starts “This backup is too large for the backup disk.”Time Machine could not complete the backup

Time Machine offers two suggestions to solve this problem:

  • Select a larger backup disk or
  • Mark the backup smaller by excluding files.

As you saw in the video above, having a backup drive just a little bit larger than the stuff you want to back up does not work. As you can see in the error message, “Time Machine needs work space on the backup disk, in addition to the space required to store backups.” This is why you can’t assume that Time Machine will back up fine just because the space available on your external drive is larger than the “Estimated size of full backup” that you’ll see in the Time Machine Options window. Time Machine doesn’t give you any insight into how much “work space” it needs but I’ve seen estimates that 20-25% extra space is required.

If you really have to use an external drive that’s just big enough to fit everything you need to back up, you can use the method I was forced to use in the video. Find one or more large folders (photos, iTunes, etc.) and use the method described above to exclude them from your backup. Remember, you are just doing this temporarily. Let Time Machine perform its first backup successfully, then go remove the items you added to the exclusion list, and then have Time Machine perform another backup. This works because the second backup will not need as much “work space” as backing up everything in the first backup. NOTE: You will have a backup of each file, but you will likely never have much history of previous versions of files. So you won’t really be getting the full benefit of using Time Machine.

How big a disk?

To get the full benefit of having many hourly, daily, and weekly historical copies of your files, I suggest getting an external drive that’s two to three times larger than your internal drive. If you could afford to buy your Mac, then you have no excuse to not buy a backup drive for it. They are dirt cheap!

There are thousands of models to choose from. You don’t absolutely have to buy one that says it’s for a Mac, but if you don’t you may have to reformat the drive before setting it up with Time Machine. If you know how to do that, great. If not, don’t worry, there are lots of drives that come already formatted for the Mac and they’ll usually brag about it in their product name or right on the box.

Prices vary but, in general, you will pay more for greater capacity and a smaller case. For instance, as of right now (October 21, 2011) on you can get a good 1 TB drive (Western Digital My Book for Mac 1 TB USB 2.0 Desktop External Hard Drive) for $86.89. Surprisingly, the 2 TB version of the same model (Western Digital My Book for Mac 2 TB USB 2.0 Desktop External Hard Drive) is only a bit more, $97.95. Yep, for about the cost of a couple grande vanilla lattes you can get double the capacity.

Or, if you find those two and half pound models too clunky, you can get a smaller package but you’ll pay about the same for less capacity. This 750 GB external drive (Western Digital My Passport for Mac 750 GB USB 2.0 External Hard Drive) is $93.81 (as of Oct 21, 2011), could easily fit in your pocket, and weighs less than seven ounces! But remember, 750 GB is only 3/4ths of 1 TB.

All these prices are sure to change in the near future so here are the current prices, live from

If history is any indication, these prices will almost certainly go down and/or drive capacities will increase. Please, do not let either of these make you delay getting an external drive if you currently have no backups!

Ejecting the right way

If you have a desktop Mac, there’s no reason to ever unplug your external drive. Just let Time Machine back up your computer whenever its on.

If you have a Mac laptop, you’ll probably want to unplug your external drive whenever you move the computer. Do not unplug your external drive unless you use the EJECT command first. You find it in the Finder’s File menu or simply right-click (or Control-click) on the external drive’s icon and choose the Eject command from the contextual menu that pops up. Whichever you do, WAIT until the icon disappears. Only then can you safely unplug the drive. Failure to follow this method could cause you to lose valuable files.

So, if you aren’t currently backing up your Mac, please do so soon. Someday you’ll be very happy you did.

[Disclaimer: If you purchase using any of the links or buttons in this article, I’ll make a small commission. Your price is unaffected.]

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